The present invention relates to stationary drying, such as for clothes drying, and particularly to a stationary drying apparatus including an air flow directed against the clothes to be dried.
Significant percentages of items that are washed are not dried in a tumble dryer. Estimates of percentages are as high as 40%. These items are typically dried hanging in ambient air or, if the danger of stretching exists, dried laying flat in ambient air. When drying in this manner, free convection is the primary mechanism of heat transfer. Free convection also carries away evaporated water in support of the necessary mass transfer.
Drying rates can be doubled or tripled in comparison to free convection when common fans or blowers are used to provide conventional parallel flow forced convection heat transfer. Heat transfer rates may also be greatly increased for conventional forced convection, however fan/blower cost will typically rise exponentially with increased heat transfer rate.
For some fabrics, drying, while initially fast, may become slower later in the drying cycle due to the need to break mechanical and chemical bonds that limit the amount of “free” water available for evaporation. Normally this binding is more easily broken as temperatures are elevated.
Drying devices have been built in the past in which items may be placed to dry in a forced convection air stream that is typically heated. For example, EP 0 933 465 discloses a stationary clothes dryer having a perforated plate for receiving a layer of clothing articles to be dried, through which a flow of heated air is directed. These drying devices include stationary supports as well as movable drawers. For example U.S. Pat. No. 5,870,836 discloses the use of porous shelf inserts that slide in horizontal slots. These devices have been effective in reducing the drying time in comparison to ambient drying, however, these designs have not reached their highest potential effectiveness. The primary reason that limitations exist in the prior art designs is the limited consideration that has been given to optimum heat transfer and air flow design. In some designs, air flow is diverted by one item to be dried such that drying of other items is effectively blocked.